Bacterial Infection

At some point, your rabbit may develop an illness or infection for which you will need to consult your veterinarian for a culture and sensitivity test.

Culture and sensitivity testing is performed if your veterinarian suspects a serious bacteria infection. The signs of such an infection may be an unrelenting sneeze, an infected abscess, or a recurring cough. Your veterinarian may also perform this test if a bacteria infection has not been resolved in response to initial antibiotic therapy. The goal of this article is to shed a little light on what a bacteria infection is, how it is diagnosed and treated by your veterinarian, and the role played by the laboratory technicians who assess the bacteria.

Determining Antibiotic Sensitivity and Resistance

Your veterinarian may use a swab to collect a sample (for example, from nasal or ocular secretions/discharge) or may collect other samples (for example, a urine sample or discharge from a skin abscess). The sample is then submitted to a bacteriology laboratory for incubation in an attempt to grow the bacteria contained in the sample. Once growth is achieved, the bacteria are isolated using a variety of culture media and growth conditions that allow the laboratory to identify the organisms in the sample. Individual bacteria are then exposed to different antibiotics applied directly to the culture plate to determine antibiotic resistance. The laboratory assesses the bacteria’s ability to grow in the presence of these antibiotics and determines a profile of antibiotic sensitivity or resistance. This information is submitted to your veterinarian and is used to determine the appropriate antibiotic to fight the bacterial infection.

Interestingly, the antibiotic testing that occurs at the laboratory uses a standardized battery of antibacterial drugs (although your veterinarian can request that the organisms be challenged with a specific antibacterial drug). These antibacterial drugs can include drugs that may not be appropriate for use in rabbits. It is your veterinarian’s responsibility to make the most clinically appropriate antibiotic choice for your rabbit. Your veterinarian must consider species-specific concerns, the bacteria’s sensitivity profile, and the overall clinical picture (for example, the site or organ that is infected, pharmacology of drug options, and several other concerns).

Aerobic and Anaerobic Bacteria

There are two types of bacteria that can affect your rabbit: aerobic and anaerobic bacteria. Aerobic bacteria are bacteria that require oxygen to grow and thrive, while anaerobic bacteria are able to grow and thrive without oxygen. Some bacteria are able to grow under either aerobic or anaerobic conditions (facultative anaerobes) while others cannot thrive in the presence of oxygen (obligate anaerobes). If your veterinarian suspects that anaerobic bacteria are present, samples are submitted in both aerobic and special anaerobic transport media. Culture conditions at the lab will then ensure the specific aerobic or anaerobic conditions are maintained throughout the culture process.

Pathogen or Normal Flora?

Certain normal bacteria are part of a healthy rabbit’s biological makeup. As part of an antibiotic treatment, your veterinarian and the bacteriology laboratory will try to distinguish between true pathogens and the normal flora as part of the decision process.

This will help minimize the suppression of your rabbit’s normal flora and maximize the impact on the pathogen.

The laboratory will often isolate several organisms from one culture, which will be used to determine whether the suspected organism is a pathogen or part of your rabbit’s normal flora. Determining which organisms represent pathogens, contaminants, or normal flora is a complex task and is often a matter of experience on the part of your veterinarian. Reference materials do exist to assist your veterinarian in making such judgments, and many veterinary bacteriology labs often employ veterinary microbiologists who can assist in making such determinations should questions arise in response to a culture profile.

Bacteria Resistance

Throughout this article we have explored how your veterinarian determines whether a bacterial infection is present in your rabbit and determines the appropriate treatment options. It is important to keep in mind that despite determining a bacteria’s sensitivity, treatment may not always be effective in resolving the infection due to certain key factors. It is essential that the antibiotic reach the infection site and that adequate blood circulation be present at the site. This allows adequate penetration and distribution of the antibiotic. When blood circulation to the site is inadequate, and depending on the conditions of the site, antibiotic treatment may not always be successful.

While the biochemical mechanisms that allow bacteria to develop antibiotic resistance are many, inappropriate antibiotic use (for example, frequency of administration, dose, and duration) is the biggest issue that causes resistance. This fact alone stresses the importance of working with a knowledgeable veterinarian you trust, who takes the time to explain your rabbit’s condition and the treatment plan.

The information contained in this article was provided by:

Dr. Keith Johnson
Carling Animal Hospital
Ottawa, Ontario.